There are known display devices, such as liquid crystal display devices and organic EL display devices, which achieved a touch screen function and a function of maintaining or improving display quality by providing optical sensor circuits on display sections of the display devices.
FIG. 27 is a view illustrating a configuration of a display device disclosed in Patent Literature 1. A display device 150 of FIG. 27 includes an image signal output circuit 152, a display section 153, a writing scanning circuit 154, a sensor scanning circuit 155, and a sensor output detection circuit 156. On the display section 153, 121N,M are arranged in matrix from a pixel circuit 1211,1, and 161N,M are arranged in matrix from a light receiving circuit 1611,1 serving as an optical sensor circuit so that the pixel circuits 121 correspond to the respective light receiving circuits 161. As illustrated in FIG. 28, each of the light receiving circuits 161 includes a sensor transistor TSE, a retention capacitor Cse, an output transistor TOUT with use of a n-channel TFT, and a reading-out transistor TRS. The light receiving circuit 161 functions as an optical sensor while the sensor transistor TSE is in an off state. In other words, in a case where the sensor transistor TSE is off, a leak current corresponding to an amount of received light is flown through a gate of the output transistor Tout. In a case where the sensor transistor TSE is off, the sensor transistor TSE has such a characteristic that a leak current is increased or decreased in accordance with the amount of the received light. That is, as the amount of the received light is larger, the leak current is increased, whereas, as the amount of the received light is smaller, the leak current is decreased. Thus, an optical detection signal depending on the amount of the received light is outputted via a sensor output line SOL with use of the light receiving circuit 161.
It is also known a configuration that achieves an optical sensor circuit with use of a PIN (P-intrinsic-N) diode, instead of an optical sensor circuit including the above transistor. FIG. 29 illustrates a configuration of a liquid crystal display device having the above configuration. The liquid crystal display device illustrated in FIG. 29 includes a PIN diode 204, a thin film transistor (TFT) 206 for retaining data, a storage capacitor (Cint) 208, and a light-blocking film 210.
The TFT 206 retains, as data, an electric signal outputted from the PIN diode 204, and is close to the PIN diode 204 so as to be connected to the PIN diode 204. The light-blocking film 210 is formed to be close to the PIN diode 204 and the TFT 206 so as to block light incident upon the PIN diode 204 and the TFT 206 from backlight. Further, it is possible to pick out, as a sensor output, a change in potential caused by charging a storage capacitor 208. The light-blocking film 210 can block light incident upon the PIN diode 204 directly from the backlight, and can prevent an off-leak current caused by allowing light to be incident upon the TFT 206 to generate carriers. Further, since the PIN diode 204 is close to the light-blocking film 210, a voltage to be applied to the light-blocking film 210 is also applied to the PIN diode 204. Note that the data is read out in a direction indicated by an arrow A. A configuration including such a PIN diode as an optical sensor circuit is disclosed in, for example, Patent Literatures 2 and 3.